A polycarbonate resin plate is excellent in terms of transparency, impact resistance and heat resistance, and thus, it is used for soundproof walls, carports, signboards, glazing materials, lighting apparatuses, etc. However, such a polycarbonate resin plate is disadvantageous in that it is easily damaged because of its low surface hardness, and thus, its intended use is limited.
Patent Literature 1 proposes a method of coating the surface of the plate with a UV-curable resin or the like, and a method of performing hard coating on a substrate, to which a polycarbonate resin and an acrylic resin have been co-extruded, in order to improve the above-mentioned disadvantage of the polycarbonate resin plate.
However, such a polycarbonate resin cannot satisfy a required pencil hardness only by the hard coating of the surface thereof, and thus, it cannot be used for a purpose for which the surface hardness is required.
Moreover, in the method of coating an acrylic resin on a surface layer, since surface hardness is improved to a certain extent, it may have a wide application range such as a front plate for information display equipment. However, according to this method, there may be a case where a large warp is generated due to a difference in water absorption properties between an acrylic resin and a polycarbonate resin in a two-layer structure consisting of the two different materials, or a difference in heat resistance including a glass transition temperature as a representative example. Accordingly, this method is inconvenient for intended uses in which environmental changes are generated.
Patent Literature 2 discloses, as a method of suppressing warp, a laminate formed by laminating a resin having a low water absorption percentage on a polycarbonate resin. However, the result 40° C./90% obtained in environmental testing is insufficient as conditions for high temperature and high humidity, and thus, it cannot be said that the performance required for low warpage properties is sufficiently evaluated. In addition, the MS resin used in this patent literature is generally considered to have low heat resistance, and thus, there may be a case where this causes a problem upon post-processing.
Moreover, as a method of suppressing warp, there is a laminate formed by laminating an acrylic resin layer on both surfaces of a polycarbonate resin layer. However, when surface impact is given to one surface of the laminate, a crack is easily generated in the acrylic resin layer on the other surface, and thus, this method may be problematic for some usage.